1. Field of the Invention
The invention relates to a novel process for recovering L-citrulline from watermelons.
2. Description of the Prior Art
In mammalian physiology, L-citrulline is a naturally occurring amino acid of the formula H2NC(O)NH(CH2)3CH(NH2)CO2H that functions in the detoxification of catabolic ammonia (urea production) and is a key element in the production of the vasodilator, nitric oxide. Moreover, arginine, the amino acid for which citrulline is an immediate precursor, is essential to several critical physiological functions such as immunostimulation and blood pressure control, in addition to its role as one of the 20 amino acids that make up proteins. However, almost all ingested free arginine is cleared by the liver and does not reach the bloodstream. In contrast, citrulline is not cleared from portal circulation and is converted to L-arginine in the kidney where it is then circulated to other organs in the body. Thus, significant attention has recently been given to the use of L-citrulline as an effective agent for arginine supplementation. Its potential therapeutic applications include short bowel syndrome, protein-energy malnutrition in aging, immunostimulation, and blood pressure control. These therapeutic uses are currently under clinical investigations (Curis et al. 2005. Amino Acids. 29:177-205).
Given its close metabolic relationship with L-arginine, L-citrulline can be found in at least small amounts in almost any living organism. In plants, citrulline is present at high levels in some Cucurbitaceae, especially the watermelon. Both the rind and flesh of watermelon contain citrulline at concentrations of 1-3 mg citrulline per g of fresh tissue (Rimando and Perkins-Veazie. 2005. J. Chromatogr. A. 1078:196-200). Citrulline's role in watermelon is believed to be a protection against oxidative stress, especially during periods of drought.
Presently, citrulline is produced in China and Japan by fermentation of special strains of the microorganism, Pseudomonas putida. The recovery of L-citrulline from watermelon has been reported, but requires rigorous solution conditions for extraction, e.g., 6 M HCl at 145° C. for 4 hr (Woo and Lee. 1995. J. Chromatogr. B 665:15-19; Rimando and Perkins-Veazie. 2005. ibid). Thus, the need remains for an improved processes for the production of L-citrulline.